Rifle Scopes Diopter, and FFP, and SFP optics...altering zero ?'s

[JWG]

I know that on a SFP optic, changing magnification *can* alter the POI, if the optic has any flaws at all in the movement of the giblets.

What about diopter? Say, if two people share a rifle for a course of fire, and prefer slightly different diopter settings, will the zero wander with BOTH the SFP and FFP, JUST the FFP, or JUST the SFP, or likely neither to any notable degree unless you're shooting in the 0.2's. ?

 

[_Windrider_]

I know that on a SFP optic, changing magnification *can* alter the POI, if the optic has any flaws at all in the movement of the giblets.

What about diopter? Say, if two people share a rifle for a course of fire, and prefer slightly different diopter settings, will the zero wander with BOTH the SFP and FFP, JUST the FFP, or JUST the SFP, or likely neither to any notable degree unless you're shooting in the 0.2's. ?

I've never seen changing magnification shift POI since you aren't moving the turrets. As for the diopter, if you zero with a reticle that is out of focus and then focus it later, this maybe could have an effect. How much, not sure. But if you adjust the diopter and parallax properly before zeroing it shouldn't matter as long as whomever uses the rifle does the same thing before firing. it doesn't matter who is shooting or what they prefer, they have to be in the same plane or you will get false information if you miss.

 

[billyburl2]

https://www.snipershide.com/shootin...up-a-ffp-rifle-scope-a-simple-psa-on-diopters
Just wondering if you have read this, covers it in pretty good detail.
And yes on all SFP scopes, the POI will drift a bit with changing of magnification. Some are worse than others...

 

[Clearlight]

I've noticed some scopes have parallax issues with large diopter adjustments .
If the diopter is wound out on my LRHS , the parallax and image quality is worse .
No such issues on other , more expensive scopes . Havnt checked POI changes
with thus in the past , but I'm curious now .

 

[JWG]

https://www.snipershide.com/shootin...up-a-ffp-rifle-scope-a-simple-psa-on-diopters
Just wondering if you have read this, covers it in pretty good detail.
And yes on all SFP scopes, the POI will drift a bit with changing of magnification. Some are worse than others...

I read it, but could not relate to it. I use scopes with fixed parallax, and the reticles are crisp across a BROAD range of diopter adjustments, the target...not so much. The trick is to match up the reticle to the target, to a true 1x in my case. Some scopes this is impossible with (VCOG), and others, it works great with, and everything appears crisp and on the same plane, at all magnifications from 1 to 8.

 

[_Windrider_]

https://www.snipershide.com/shooting/forum/...sa-on-diopters
Just wondering if you have read this, covers it in pretty good detail.
And yes on all SFP scopes, the POI will drift a bit with changing of magnification. Some are worse than others...

If it's shifting it's because you didn't adjust the parallax. If the diopter is adjusted properly and the reticle is focused for your eye, changing magnification won't alter POI as long as you adjust the parallax. If changing diopter focus affected POI, company's like nightforce wouldn't have locking diopters.

Its parallax error.

focus reticle.
Set magnification
adjust parallax
shoot

chamge mag
adjust parallax
shoot

Change mag
adjust parallax
shoot

the diopter shouldn't need to be adjusted once you have it set for your eye. If someone else uses your rifle and they have different vision and they don't adjust the diopter for them, yes there could be a shift because the reticle isn't focused.

 

[billyburl2]

If it's shifting it's because you didn't adjust the parallax. If the diopter is adjusted properly and the reticle is focused for your eye, changing magnification won't alter POI as long as you adjust the parallax. If changing mag affected POI, company's like nightforce wouldn't have locking diopters.

Its parallax error.

focus reticle.
Set magnification
adjust parallax
shoot

chamge mag
adjust parallax
shoot

Change mag
adjust parallax
shoot

the diopter shouldn't need to be adjusted once you have it set for your eye. If someone else uses your rifle and they have different vision and they don't adjust the diopter for them, yes there could be a shift because the reticle isn't focused.

On a FFP scope you are mostly correct. On a SFP it is described well in this thread:
https://www.snipershide.com/shootin...int-of-aim-shift-when-changing-power-on-scope

 

[_Windrider_]

On a FFP scope you are mostly correct. On a SFP it is described well in this thread:
https://www.snipershide.com/shooting/forum/...power-on-scope[/QUOTE

Again, all the diopter does is focus a reticle.

this thread is about diopter adjustment changing POI, not necessarily about magnification. In the thread you posted, sandwarrior did a decent job explains why the mechanics and technology and money limitations create a shift when magnification changes. I'm not disputing a POI shift happens when you change the mag, I should have been more clear, but if you can see the shift it's because you didn't adjust the parallax properly. If it's a 1/2 MOA rifle at 100 it should be that 1000 regardless of the power. Point being you won't notice the shift on the mag change alone. But if you fail to adjust parallax, you will.

 

[G17C]

Another (perhaps not completely related) observation;

I've been near-sighted all of my life and have worn corrective lenses for that condition for nearly 60 years. As I've grown older I've become far-sighted as well (need reading glasses) which has actually made my distance vision better. For those of you in the same or similar boat, try shooting without your corrective lenses. For me, I can get the reticle razor-sharp with the ocular adjustment and my view through the scope crystal clear with the focus/parallax adjustment. One less lens to have to look through, one less lens to get smudged, dirty or covered in sweat, and no struggle trying to keep the corrective lens in the line-of-sight while shooting prone.

 

[_Windrider_]

Another (perhaps not completely related) observation;

I've been near-sighted all of my life and have worn corrective lenses for that condition for nearly 60 years. As I've grown older I've become far-sighted as well (need reading glasses) which has actually made my distance vision better. For those of you in the same or similar boat, try shooting without your corrective lenses. For me, I can get the reticle razor-sharp with the ocular adjustment and my view through the scope crystal clear with the focus/parallax adjustment. One less lens to have to look through, one less lens to get smudged, dirty or covered in sweat, and no struggle trying to keep the corrective lens in the line-of-sight while shooting prone.

I wear contacts when I shoot most of the time. But I try to buy really good glasses for this reason. Like a scope you can really see the difference. Why buy a S&B scope for 3500k and loook through garbage glasses. For me Oakley/ESS have about the best glass around. It's all I use these days.

 

[Deleted member 10043]

If it's shifting it's because you didn't adjust the parallax. If the diopter is adjusted properly and the reticle is focused for your eye, changing magnification won't alter POI as long as you adjust the parallax. If changing diopter focus affected POI, company's like nightforce wouldn't have locking diopters.

Its parallax error.

focus reticle.
Set magnification
adjust parallax
shoot

chamge mag
adjust parallax
shoot

Change mag
adjust parallax
shoot

the diopter shouldn't need to be adjusted once you have it set for your eye. If someone else uses your rifle and they have different vision and they don't adjust the diopter for them, yes there could be a shift because the reticle isn't focused.

what about scopes with fixed parallax and the sight picture is out of focus or vice versa?

 

[Deleted member 10043]

I wear contacts when I shoot most of the time. But I try to buy really good glasses for this reason. Like a scope you can really see the difference. Why buy a S&B scope for 3500k and loook through garbage glasses. For me Oakley/ESS have about the best glass around. It's all I use these days.

That is what the "diopter" is for. Some people refer to it as the prescription.

 

[_Windrider_]

what about scopes with fixed parallax and the sight picture is out of focus or vice versa?

Obviously I can't account for every nuance. However I still contest that adjusting the diopter will not effect POI.

 

[_Windrider_]

That is what the "diopter" is for. Some people refer to it as the prescription.

Yep, but for some it's not enough.

 

[Deleted member 10043]

Then it us just a rear focus on a fixed parallax scope? Which would be more important, a clear picture of the target or reticle?

 

[_Windrider_]

Then it us just a rear focus on a fixed parallax scope? Which would be more important, a clear picture of the target or reticle?

Reticle

 

[Deleted member 10043]

To the OP, it really doesn't matter because we should not be messing with the prescription/diopter once it is set for us. Giving it to another user and letting him mess with the diopter to suit him is only going to force you to reset it for yourself. Forcusing the reticle is just for you and has nothing to do with POI. The other user can get by with a blurry reticle if the two of you have completely drastic different eyesight.

Parallax must be different as mentioned already. Even with a fixed parallax scope that rear eyepiece adjustment is for the reticle and not the target. Most of these have a lock ring for it. The simple Leupold Rifleman series are a good example and instructions are clear enough...

FOCUSING THE RETICLE
Secure the scope and firearm in a firm rest . Safely point the scope at a light colored background.

1 . If the eyepiece has a lockring, grasp the eyepiece with your hand and rotate counterclockwise until the lock is loose .
2 . Look through the scope while pointed at a light colored background . Look away every so often to relax your eye between focus checks . Rotate the eyepiece and recheck focus repeatedly until the reticle is sharp .
3 . If your eyepiece has a lockring, retighten the lockring against the eyepiece .

So, clearly on these fixed parallax scopes your targets are not going to be in focus for any targets before or after the parallax setting. Let's say 50, 100, 150 yards depending on the scope setting from the factory.

With that in mind, is it really necessary for a parallax adjustment knob for targets between 100- 500 meters or so? Wouldn't repeat-ability be improved if we set the parallax at around 250 and leave that alone no different than the diopter setting? Wouldn't the constant adjustment to the parallax knob or AO introduce parallax error on the part of the user due to such things as time constraints on targets at different distances from the shooter?

This is probably one of the most confusing topics I see on this forum and everybody is not on the same page.

 

[JWG]

To the OP, it really doesn't matter because we should not be messing with the prescription/diopter once it is set for us. Giving it to another user and letting him mess with the diopter to suit him is only going to force you to reset it for yourself. Forcusing the reticle is just for you and has nothing to do with POI. The other user can get by with a blurry reticle if the two of you have completely drastic different eyesight.

Parallax must be different as mentioned already. Even with a fixed parallax scope that rear eyepiece adjustment is for the reticle and not the target. Most of these have a lock ring for it. The simple Leupold Rifleman series are a good example and instructions are clear enough...

FOCUSING THE RETICLE
Secure the scope and firearm in a firm rest . Safely point the scope at a light colored background.

1 . If the eyepiece has a lockring, grasp the eyepiece with your hand and rotate counterclockwise until the lock is loose .
2 . Look through the scope while pointed at a light colored background . Look away every so often to relax your eye between focus checks . Rotate the eyepiece and recheck focus repeatedly until the reticle is sharp .
3 . If your eyepiece has a lockring, retighten the lockring against the eyepiece .

So, clearly on these fixed parallax scopes your targets are not going to be in focus for any targets before or after the parallax setting. Let's say 50, 100, 150 yards depending on the scope setting from the factory.

With that in mind, is it really necessary for a parallax adjustment knob for targets between 100- 500 meters or so? Wouldn't repeat-ability be improved if we set the parallax at around 250 and leave that alone no different than the diopter setting? Wouldn't the constant adjustment to the parallax knob or AO introduce parallax error on the part of the user due to such things as time constraints on targets at different distances from the shooter?

This is probably one of the most confusing topics I see on this forum and everybody is not on the same page.

So basically...set diopter AT the parallax range the scope is fixed for, and then "deal with it" regarding any discrepancy otherwise in clarity?

 

[Deleted member 10043]

Yes, at lower distances the parallax error is rather small. At longer distances we set it to infinity anyway. There is a small formula to estimate the error if you want to tinker with it.

But, this brings me back to the shooter diopter setting. If it does not effect POI then what is so terribly wrong with moving it to focus on the target and still have a good reticle picture as well.

Parallax error estimated...



Results using your inputs (below):
50mm Objective lens and 375-yard fixed parallax setting

Range (yards)	Error (mm)	Error (mil)	Error (inches)	Error (moa)
100	18.333	0.200	0.722	0.689
200	11.667	0.064	0.459	0.219
300	5.000	0.018	0.197	0.063
400	1.667	0.005	0.066	0.016
500	8.333	0.018	0.328	0.063
600	15.000	0.027	0.591	0.094
700	21.667	0.034	0.853	0.116
800	28.333	0.039	1.115	0.133
900	35.000	0.043	1.378	0.146
1000	41.667	0.046	1.640	0.157

 

[FourT6and2]

Hey, remember that time I asked this same question on the Scout site and I got chewed out for using the word "diopter"? Yeah. Good times.

I literally had to screen shot instructions manuals from a bunch of scope manufacturers to "prove" it was a real word and that it was used in the firearms industry. My, we've all come a long way since the switch.

 

[_Windrider_]

Hey, remember that time I asked this same question on the Scout site and I got chewed out for using the word "diopter"? Yeah. Good times.

I literally had to screen shot instructions manuals from a bunch of scope manufacturers to "prove" it was a real word and that it was used in the firearms industry. My, we've all come a long way since the switch.

Who did that? Were they saying it's called the occular and not the diopter?

 

[FourT6and2]

Who did that? Were they saying it's called the occular and not the diopter?

Yeah, pretty much haha. People were like, "WTF is a diopter???? You idiot."

 

[Deleted member 10043]

That was probably me. Anyway, does it affect the POI?

 

[_Windrider_]

That was probably me. Anyway, does it affect the POI?

Well if it's zeroed out of focus and then refocused it could. If you are trying to zero and that reticle isn't nice and crisp, you could be adjusting more or less than you actually need to to get your zero. Then the next time you shoot you make that reticle nice and crisp it could shift because you made an incorrect zero correction. Probably won't see it at 100, at a 1000 maybe.

 

[Deleted member 10043]

I'm referring to out to 500 - 600 yards. Just getting close on parallax won't introduce enough error to notice. I tend to agree on the diopter. A small fast rear eye focus there on the target shouldn't be a problem. We use too much stuff out to 800 yards. Things like spin drift, CE, humidity, and so forth. Getting anal about parallax and rear eye focus falls in the same category. The time to get anal is at ELR. Shooting out to midrange should be fun without dicking around with useless information and minute adjustments.

 

[_Windrider_]

Well according your table up there at 1k we are talking 4.1 cm. Yeah I'd say it probably doesn't matter. But it also depends on the size of your target. Bigger targets are more forgiving.

 

[_Windrider_]

I'm referring to out to 500 - 600 yards. Just getting close on parallax won't introduce enough error to notice. I tend to agree on the diopter. A small fast rear eye focus there on the target shouldn't be a problem. We use too much stuff out to 800 yards. Things like wind drift, CE, humidity, and so forth. Getting anal about parallax and rear eye focus falls in the same category. The time to get anal is at ELR. Shooting out to midrange should be fun without dicking around with useless information and minute adjustments.

Yes I agree. I don't even care about humidity. SD, depending on bullet, is neglible inside 1k. Focus on fundamentals and reading the wind and just shoot.

 

[Deleted member 10043]

I wrote wind drift but meant spin drift. All this stuff is by popular demand. The only time I experienced a parallax error was shooting 1moa silhouette at 500 meters with the parallax set at two hundred. Basically, turned into a .7 moa target.

 

[spife7980]

Well according your table up there at 1k we are talking 4.1 cm. Yeah I'd say it probably doesn't matter. But it also depends on the size of your target. Bigger targets are more forgiving.

Yeah but that's with a 375 yard parallax which is mid range and neither the near nor far would look very good. With a fixed 100 yard setting which most fixed parallax scopes are it makes a fair amount of difference when stretched out to greater distances and thusly don't look as good out that far either.

Functionally it may be better in long range scenarios but scopes that have fixed parallax aren't typically geared towards long range stuff further than a couple hundred yards. If they were they would have adjustable parallax. Since you have adjustable parallax you can dial it out and it becomes a non concern. Most scopes that have adjustable parallax in a manner that would be considered long range oriented so as to have those features will be of sufficient quality that the diopter will shift point of aim. I suspect my leupold vx3 does indeed shift with a change but how much I'm not sure of, haven't bothered to sit it down and actually test so it's not a large amount and as I have glasses I locked it down solid so other people couldn't mess it up. I know the tasco I had on a pellet gun as a child did for certain.

 

[Deleted member 10043]

Parallax set at 200 yards adds up to a .1 mil error at 100 and 400-1000 yards. On a good scope if you set the parallax on 500 for a 500 yard target and then adjust it a little to focus on the target than that should be immaterial. Same thing for a non-locking rear focus.

Here is a good question, that answer for which I don't know. A calculated parallax error can be negative or positive to indicate which side of the target the error is occurring. So, a positive would be which side?

 

[_Windrider_]

Parallax set at 200 yards adds up to a .1 mil error at 100 and 400-1000 yards. On a good scope if you set the parallax on 500 for a 500 yard target and then adjust it a little to focus on the target than that should be immaterial. Same thing for a non-locking rear focus.

Here is a good question, that answer for which I don't know. A calculated parallax error can be negative or positive to indicate which side of the target the error is occurring. So, a positive would be which side?

usually, positive is to the right of zero, in math equations. look at an X-Y axis, left and down are always negative values. a reticle is just an X-Y axis.

 

[Deleted member 10043]

That is easy enough. Thanks.

 

[scudzuki]

The reason an SFP scope can experience a zero shift when changing magnifications is because the second focal plane glass the reticle is etched on (or the wire reticle if so equipped) is moving in the erector assembly when magnification is changed.
A reticle in the FFP is not moved when changing magnification.
Since you are not moving the reticle lens (or wire) when adjusting the diopter you will not see a zero shift, but the entire FOV could in theory move, the reticle moving along with the target.

 

[scudzuki]

Yeah, pretty much haha. People were like, "WTF is a diopter???? You idiot."

Ocular = the eyepiece, as in, the entire assembly.

Technically there is not "a" diopter, even though that's what many (including myself) call the "diopter adjuster". Diopter is a unit of measurement that represents the amount a particular lens bends light (refractive index). In the specs for a scope you may see a range of diopter values available from that scopes diopter adjuster. The role of the adjuster is to enable the shooter to adjust to a diopter value that allows the focal plane of the shooter's eye to fall coincident with the reticle plane, bringing the reticle into focus.

At that point, dialing the parallax adjustment to bring the target into focus makes the two focal planes coincident (the same distance from the shooters eye), so the target is focused on the same plane as the reticle, and parallax error is eliminated.

Remember, parallax error happens when the focal plane the target falls on is in front of or behind the reticle plane.